Blood Beach (1980) Something Under The Sand Is Eating Local Sunbathers Whole

This is a slightly extended version that includes 2 VERY brief bloody monster claws grabbing victims under the sand, that only appeared in the German VHS version. (possibly clip-inserts from another movie??)
A kind of reverse spin on the popular JAWS movies of the era.
Something very big beneath Santa Monica & Venice Beach is gobbling up beach goers & sunbathers.
Starring: Burt Young (Rocky) & John Saxon (Nightmare On Elm Street)
I remember the TV trailer scared the hell out of me as a kid.
Plot:
Something or someone is attacking people one by one on the beach. Some of them are mutilated, but most of them are sucked into the sand, disappearing without a trace. What is the creature responsible? Where does it live, and where did it come from? And is there any chance of it reproducing? Meanwhile, David Huffman and Mariana Hill are once-almost-married old friends, reunited over the death of her mother on the beach, and searching for clues in the abandoned buildings where they used to play when they were young.